In an exhaust gas recirculation (EGR) apparatus, it is necessary to restrict a heat transfer from a recirculating exhaust gas to a motor or a reduction gears. The recirculating exhaust gas is referred to as EGR gas, hereinafter. Japanese patent No. 4687540 (US-2007-0240690A1) describes an EGR apparatus which is provided with a housing and a nozzle. The housing accommodates a motor and reduction gears. The nozzle forms a passage for EGR gas with the housing and has a valve body. An air layer is formed between the nozzle and the housing. The air layer restricts a heat transfer from the EGR gas to the motor and the reduction gears.
In a case that a valve body is arranged upstream of an EGR gas cooler in order to accelerate a softening of solidified deposits around the valve body, the EGR gas of high temperature flows through the passage, so that a temperature difference between the EGR gas and the housing becomes larger. As a result, it is likely that heat quantity transferred from the EGR gas to the motor and the reduction gears through the housing is increased.
FIG. 10 shows a part of a conventional EGR apparatus 100 which is provided with a driving portion 101 and a passage-forming portion 102. The driving portion is comprised of a housing which accommodates a motor and reduction gears. The passage-forming portion 102 defines a passage for EGR gas and accommodates a valve body. The driving portion 101 and a passage-forming portion 102 are fastened by a bolt 103.
A heat insulating material 106 is arranged between a passage-side fastening portion 104 of the driving portion 101 and a drive-side fastening portion 105 of the passage-forming portion 102. The heat insulating material 106 restricts a heat transfer from the EGR gas to the driving portion 101 through the passage-forming portion 102. However, the heat insulating material 106 is not always enough to restrict the heat transfer.